Main Petrochemicals. Chapter 2

Chapter 2 Main petrochemicals 1 Introduction Petrochemicals in general are compounds and polymers derived directly or indirectly from petroleum used in the chemical market as plastics, synthetic fibers, synthetic rubber, detergents, nitrogen fertilizers, paints, adhesives, aerosols, insecticides, and pharmaceuticals. The primary raw materials for the production of petrochemicals are natural gas and crude oil. The petrochemical industry is mainly based on three types of intermediates: • C2-C4 olefins, C6-C8 aromatics, and synthesis gas. 2 Cont’d… The C2 and heavier hydrocarbons from these two sources (natural gas and crude oil) can be converted to light olefins suitable as starting materials for petrochemicals production. An aromatic-rich mixture obtained from catalytic reforming and cracking processes, further extracted to obtain the required aromatics for petrochemical use. LPGs (C3-C4), natural gas and refinery gas streams catalytically converted into a liquid hydrocarbon mixture rich in C6-C8 aromatics. Synthesis gas (generated by steam reforming of either natural gas or crude oil fractions) is the precursor of two big-volume chemicals, (ammonia and methanol). 3 Chemical conversions The chemical conversion is defined as the industrial processing of chemical raw materials into products of enhanced industrial value. Petrochemical industries employ both chemical conversions and physical changes to convert the basic raw materials into petrochemicals. The basic chemical conversions employ in the petrochemical industries are oxidation, nitration, reduction, halogenations, isomerization, alkylation, acylation, etc. 4 Raw Materials for Petrochemicals • Natural gas and crude oils are primary raw materials for the manufacture of petrochemicals. • Secondary raw materials (intermediates) are light HC cpds such as CH4 and C2H6, or heavier HC mixtures such as naphtha or gas oil are obtained from crude oils through different processing schemes. Petrochemicals from CH4 CH4 is not reactive under normal conditions. Chlorination is possible only by thermal/photochemical initiation.  It can be partially oxidized with a limited amount of O2 or in presence of steam to a syn gas mixture. 5 Cont’d…. Activated alumina or clay is used as the catalyst at  675°C and 2 atm. The process starts by vaporizing pure sulfur, mixing it with methane, and passing the mixture over the alumina catalyst CH4(g) + 2S2(g)  CS2(g) + 2H2S(g) ΔH°298 = +150 KJ/mol 2H2S(g), a co-product, is used to recover sulfur by the Claus reaction. 6 HCN 2CH4 + 2NH3 + 3O2 → 2HCN + 6H2O (Andrussaw process) in the presence of a Pt-Rh alloy at 1100°C. Used to synthesize acrylonitrile and adiponitrile which are used for plastic and synthetic fiber production.  Degussa process, reaction of ammonia with methane in absence of air using Pt-Al-Ru alloy as a catalyst at 1200°C. CH4 + NH3 + 251 KJ → HCN + 3H2  It can also be produced: NH3 + CH3OH + O2 → HCN + 3H2O  Copper nitrate catalyst at about 70°C and atmospheric pressure is used to produce the oxyamides. 7 Chloromethanes  The successive substitution of methane hydrogens with chlorine produces a mixture of four chloromethanes (CH3Cl, CH2Cl2, CHCl3 & CCl4).  The reaction is initiated by chlorine free radicals obtained via the application of heat(industrially widely used) or light. Cl2 (hv) → 2Cl• CH4 → 3 + HCl •CH + Cl → CH Cl + Cl• 3 2 3 Cl•+ CH3Cl → •CH2Cl + HCl •Cl+ •CH • Cl + Cl → CH Cl + Cl 2 2 2 2 CH2Cl2 + Cl• → •CHCl2 + HCl •CHCl + Cl → CHCl + •Cl 2 2 3 •CH Initiation propagation Termination: combining two radicals to give a stable product. 8 Uses of Chloromethanes The major use of methyl chloride is to produce silicon polymers For synthesis of tetra-methyl Pb as a gasoline octane booster, a methylating agent in methyl cellulose production, a solvent and a refrigerant as paint remover and as degreasing solvent, a blowing agent for polyurethane foams, Chloroform also used to synthesize tetrafluoroethylene, which is polymerized to a heat resistant polymer (Teflon): CHCl3 + 2HF→ CHClF2 +2HCl 2CHClF2 → CF2═CF2 + 2HCl 9 Petrochemicals Based on Ethylene Ethylene is known as the “king of petrochemicals” because more commercial chemicals are produced from ethylene than any other intermediate. This unique position of ethylene among other hydrocarbon intermediates is due to: Its simple structure with high reactivity Relatively inexpensive Easily produced from any hydrocarbon source through steam cracking in high yields Less by-products generated from ethylene reactions with other compounds than from other olefins. 10 Cont’d… 11 Chemicals Based on Propylene Is “the crown prince of petrochemicals,” is second to ethylene as the largest-volume hydrocarbon intermediate for the production of chemicals. propylene is a reactive compound that can react with many common reagents used with ethylene. But the structural differences between these two olefins result in different reactivities toward these reagents. For example, direct oxidation of propylene using oxygen does not produce propylene oxide as in the case of ethylene. Instead, an unsaturated aldehyde, acrolein is obtained (ease of oxidation of allylic hydrogens ). 12 Cont’d…. 13 Chemicals based on n-butylenes • The three isomers of n-butenes are 1-butene, cis-2-butene, and trans-2butene. This gas mixture is from the olefinic C4 fraction of catalytic cracking and steam cracking processes after separation of isobutene. • The mixture of isomers may be used directly for reactions that are common for the three isomers to produce the same intermediates and products. • Alternatively, the mixture may be separated into two streams, one constituted of 1-butene and the other of cis and trans-2-butene mixture. Each stream produces specific chemicals. 14 Oxidation of butenes Oxidized to different products depending on the reaction conditions and the catalyst. The three commercially important oxidation products are acetic acid, maleic anhydride, and methyl ethyl ketone. Acetic acid Oxidation reaction via vapor-phase catalytic process at approximately 270°C over a titanium vanadate catalyst:  It can be produced also by reacting a mixture of n-butenes with acetic acid over an ion exchange resin. The formed sec-butyl acetate is then oxidized to yield acetic acid: 15 Acetic anhydride • Produced from acetic acid occurs via the intermediate formation of ketene where one mole of acetic acid loses one mole of water: , Methyl ethyl ketone The production of MEK from n-butenes is a liquid-phase oxidation process similar to that used to produce acetaldehyde from ethylene using a Wacker-type catalyst (PdCl2/CuCl2). As selective solvent in dewaxing lubricating oils  used to synthesize MEK peroxide (a polymerization catalyst used to form acrylic and polyester polymers) and methyl pentynol by reacting with acetylene 16 17 Petrochemicals Based on benzene, toluene and xylene (BTX) • The primary sources of BTX are catalytic reforming & cracking, pyrolysis gasoline from steam cracking and from coal liquids. 18 Petrochemicals based on Toluene Toluene is similar to benzene as a mononuclear aromatic, but it is more active due to presence of the electron-donating methyl group. Due to this, toluene is much less useful than benzene because it produces more polysubstituted products. Can be converted to benzene via de-alkylation or disproportionation. Dealkylation of toluene - is essentially a Hydrocracking reaction favored at higher temperatures and pressures via hydrogenationdehydrogenation catalyst (nickel). De-alkylation Disproportionation reaction are 450–530°C and 20 atm by using a mixture of CoO-MoO3 on aluminosilicates/alumina catalysts. Disproportionation 19 Oxidation of toluene Used to synthesize Polycaprolactum, N6, Phenol from Benzoic Acid through action of a copper salt which is reoxidized by air, functions as a real catalyst. The overall reaction is:- 20 Cont’d… • Phenol and acetone produce bis-phenol A, an important monomer for epoxy resins and polycarbonates. It is produced by condensing acetone and phenol in the presence of HCI, or by using a cation exchange resin. bis-phenol A 21 Terephthalic Acid from Benzoic Acid It is an important monomer for producing polyesters  Its main route is the catalyzed oxidation of paraxylene  It can also be produced from benzoic acid by a disproportionation reaction of potassium benzoate in the presence of carbon dioxide.  Cobalt acetate promoted with either NaBr or HBr is used as a catalyst in an acetic acid medium, at 200 oC and 15 atm. 22 Cumene Synthesis  The main process for producing cumene is a synthetic route where benzene is alkylated with propylene to isopropylbenzene.  Either a liquid or a gas-phase process is used for the alkylation reaction.  In the liquid-phase process, low temperatures and pressures are used with sulfuric acid as a catalyst. 23